Minor gene effect of leptin receptor variant on the body weight in KK/Ta mice

Role of EphB2/ephrin‑B1 signalling in the development and progression of obesity‑associated colorectal cancer

Obesity is a major problem worldwide and has been associated with colorectal cancer development, among other diseases. Ephrin receptors and ligands play an important role in the turnover of the intestinal mucosa and intestinal crypt compartmentalization. It has been hypothesised that obesity-induced inflammation affects ephrin signals, leading to carcinogenesis. Therefore, the aim of the present study was to assess the relationship between Eph-ephrin B signalling, obesity and obesity-associated colorectal cancer. An azoxymethane-induced obesity-associated cancer KKAy mouse model developed in our prior study was used. A total of 46 patients with consecutive colorectal cancer and 48 tumours were analysed. Immunohistological analyses were performed in mouse and human samples, and immunoreactive scores (IRS) were determined. KKAy mice were significantly more prone to cancer development compared with control C57/BL mice (2/15 in C57/BL vs. 10/10 in KKAy; P<0.001). TUNEL assay revealed a lower number of apoptotic cells in normal mucosa of KKAy mice (8.8% in C57/BL vs. 3.2% in KKAy; P<0.001) and obese patients (9.2% with BMI <25 vs. 3.6% with BMI ≥25; P=0.021). Immunohistological analysis revealed that ephrin-B1 was downregulated in normal mucosa from KKAy mice and obese patients (IRS, 2.86 with BMI <25 vs. 6.00 with BMI ≥25; P=0.002). Moreover, EphB2 was downregulated in tumours from KKAy mice and obese patients (IRS, 6.58 with BMI <25 vs. 3.83 with BMI ≥25; P<0.001). The distribution of infiltrated macrophages corresponded to the MCP-1 expression pattern in KKAy mice, and the number of macrophages was also significantly higher in those mice (36.3 in C57/BL vs. 120.0 in KKAy; P=0.029). The findings suggested that obesity results in disruption of EphB2/ephrin-B1 signalling, promoting colorectal cancer development and progression.

Interleukin-13 and its signaling pathway is associated with obesity-related colorectal tumorigenesis

The incidence of colorectal cancer (CRC) has been on the rise, which is linked to the increasing prevalence of obesity, based on global epidemiological evidence. Although chronic inflammation is implicated in tumor development, the mechanisms underlying obesity‐associated CRC remain unknown. Here, we sought to identify the inflammatory cytokines and their roles in obesity‐related colorectal tumorigenesis using cytokine array analyses in a mouse model. Colorectal tumorigenesis was induced through i.p. injection of azoxymethane once a week for 6 weeks in 6‐week‐old female WT C57Black/6J mice and the obesity diabetes model mouse KK/TaJcl, KK‐Ay/TaJcl. The formation of aberrant crypt foci and colorectal tumors were more frequent in obese mice compared with WT mice, and both serum interleukin (IL)‐13 and IL‐13 receptor (R) expression in the normal intestinal mucosal epithelium were significantly increased in the obese mice. Furthermore, addition of IL‐13 to a human CRC cell line and a human colon organoid culture altered the phenotype of intestinal epithelial cells. Knockdown experiments further revealed that IL‐13Rα1 dominantly induced mucosal proliferation. Collectively, These results suggest an association between anti‐inflammatory cytokines and colorectal carcinogenesis, and provide new research directions for cancer prevention strategies. In particular, inflammation provoked by obesity, notably by increased expression of the cytokine IL‐13, could play an important role in the carcinogenesis of obesity‐related CRC.

High susceptibility to azoxymethane-induced colorectal carcinogenesis in obese KK-Ay mice

Obesity is associated with colon carcinogenesis. However, not much information is available regarding the mechanisms of obesity-associated colorectal cancer, and there are only few useful animal models for investigating the underlying mechanism between obesity and colorectal cancer. KK-A(y) mice exhibit severe obesity. Amount of visceral fat assessed by micro-computed tomography was almost 15 times higher than that of same aged C57BL/6J mice. Treatment with azoxymethane (AOM; 200 μg/mouse injected once a week for 3 times) resulted in markedly increased colon aberrant crypt foci (ACF) development (≈70 ACF/mouse) in KK-A(y) mice compared with lean C57BL/6J mice (≈9 ACF/mouse). Moreover, administration of AOM at a dose of 200 μg/mouse once a week for 6 times developed colorectal adenocarcinomas within only 7 weeks after the last AOM injection. The incidence of adenocarcinoma was 88% in KK-A(y) mice and was markedly higher than the 4% observed in C57BL/6J mice. The number of tumors/mouse was 7.80 in KK-A(y) mice and also markedly higher than the 0.12 in the C57BL/6J case. Interestingly, adenocarcinomas were observed in most of the AOM-treated KK-A(y) mice along with remarkable tumor angiogenesis, and some showed submucosal invasion. These results indicate that the KK-A(y) mouse, featuring intact leptin and leptin receptor Ob-Rbl, could be a useful animal model to investigate obesity-associated cancer.